Field of the Invention
The present invention generally relates to Micro-Electrical-Mechanical System (MEMS) microphone, in particular, to a MEMS microphone with effects of dust resistance.
Description of Related Art
The MEMS microphone is a microphone device with rather tiny size and is fabricated by semiconductor fabricating processes, so that it can be connected to integrated circuit in semiconductor fabricating processes.
FIG. 1 schematically illustrates a conventional MEMS microphone. In FIG. 1, the conventional MEMS microphone includes a MEMS structure 101. The MEMS structure 101 includes a substrate 100. The substrate 100 can be semiconductor substrate, for example, such as silicon substrate. By using photolithographic and etching processes in semiconductor fabricating processes, a cavity 112 is formed in the substrate 100 for receiving the external acoustic source.
The micro capacitor 104 includes a diaphragm 108 and a backplate 106, and a chamber 124 is formed from the space between the diaphragm 108 and the backplate 106. The chamber 124 is usually filled with air, which serves as the acoustic medium. Thus, the diaphragm 108 and the backplate 106 form a micro capacitor 104, having corresponding capacitance. The backplate 106 includes conductive material, such as polysilicon, and is formed with a plurality of venting holes 110 to connect to the cavity 112, so that the cavity 112 can extend to the diaphragm 108. This, when the cavity 112 receive the acoustic source, the diaphragm 108 can sense the acoustic source and then vibrates, resulting in variance of capacitance. The MEMS microphone can provide the signal with the variance of capacitance. The integrated circuit or system, externally connected to the MEMS microphone, can detect out the content of the acoustic source, according to the signal with the variance of capacitance.
In the semiconductor fabrication for fabricating the micro capacitor 104, the photolithographic and etching processes involve the dielectric layer for auxiliary function to be performed. The residue of dielectric material is indicated by the dielectric layer 102. The dielectric layer 102 can be used to hold the diaphragm 108. The one with ordinary skill in the art can understand that fabrication process to form the micro capacitor 104 by using the dielectric layer 102. The details are not further described here.
In addition, in order to protect the diaphragm 108 and maintain the sensitivity of the diaphragm 108, a capping structure 114 is formed over the dielectric layer 102 at another side opposite to the side having the substrate 100. The capping structure 114, for example, uses a glue layer 116 to adhere to the dielectric layer 102. The capping structure 114 has an indent space 120 corresponding to the cavity 112. The indent space 120 is sufficiently large to allow that the vibration of the diaphragm 108 is not significantly restricted. Furthermore, the capping structure 114 also has interconnect structure 118, for example, including conductive pad and conductive plug, so the electric signal sensed by the micro capacitor 104 can be outputted to the external integrated circuit for subsequent use.
As investigating into the conventional MEMS microphone above by the invention, the cavity 112 of the substrate 100 is directly connected to the external ambiance. When micro-particles 128 enter the cavity 112, some of the micro-particles 128 with relative smaller size may further pass the venting holes 110 and enter the chamber 124 between the backplate 106 and the diaphragm 108. This phenomenon would reduce the vibration of the diaphragm 108 during sensing the acoustic source, or even cause the diaphragm 108 to be incapable of sufficient vibration, resulting in malfunction.
FIG. 2 schematically illustrates another conventional MEMS microphone. In FIG. 2, the MEMS structure 202 of another design of the conventional MEMS microphone 202 is similar to the MEMS structure 101 in FIG. 1 but the packaging structure as a whole is different. The MEMS structure 202 is disposed on the cover plate 200. This cover plate 200 can be a circuit board, for example, including the interconnect structure 204, so the MEMS structure 202 is involved in the bonding step under the packaging process, in which the bonding wire 206 electrically connects the MEMS structure 202 to the interconnect structure 204 of the cover plate 200. As a result, the sensing signal from the MEMS structure 202 can be outputted, and provide the signal for use by the externally-connected integrated circuit or system.
To protect the MEMS structure 202, having the diaphragm 108 and the bonding wire 206, the capping structure 210 is disposed on the cover plate 200 and covering over the MEMS structure 202. A space between the capping structure 210 and the MEMS structure 202 allows the diaphragm 108 to vibrate as designed at the desired sensitivity. For this conventional MEMS microphone, the cover plate 200 has an acoustic hole 208, which is directly connected to the cavity 112 to receive the acoustic source. As a result from investigating to this MEMS microphone in the invention, the acoustic hole 208 is directly connected to the cavity 112. In this manner like the micro-particles 128 in FIG. 1, the micro-particles 128 may enter the chamber 124 and then cause malfunction to the diaphragm 108.